AlSi9 Micro

ENGINEERING TRANSACTIONS • Engng. Trans. • 61, 3, 197–218, 2013Polish Academy of Sciences • Institute of Fundamental Technological Research (IPPT PAN)

National Engineering School of Metz (ENIM)

The Structure Analysis of Secondary (Recycled) AlSi9Cu3Cast Alloy with and without Heat Treatment

Lenka HURTALOVA, Eva TILLOVA, Maria CHALUPOVA

University of ZilinaFaculty of Mechanical Engineering, Department of Material Engineering

Univerzitna 1, 010 26 Zilina, Slovakiae-mail: [email protected]

Al-Si alloys are very universal materials, comprising of from 85% to 90% of the aluminiumcast parts produced for the automotive industry (e.g. various motor mounts, engine parts,cylinder heads, pistons, valve retainer, compressor parts, etc.). Production of primary Al- alloysbelong to heavy source fouling of life environs. Care of environment of aluminium is connectedto the decreasing consumption of resource as energy, materials, water, and soil, and with anincrease in recycling and extension life of products in industry. Recycled (secondary) aluminiumalloys are made out of Al-scrap and workable Al-garbage by recycling. The automotive castsfrom aluminium alloys are heat treated for achieving better properties. Al-Si alloys containmore addition elements, that form various intermetallic phases in the structure. They usuallycontain a certain amount of Fe, Mn, Mg, and Zn that are present either unintentionally, or theyare added deliberately to provide special material properties. These elements partly go into thesolid solution in the matrix and partly form intermetallic particles during solidification whichaffect the mechanical properties. Controlling the microstructure of secondary aluminium castalloy is therefore very important.

Key words: secondary Al alloy, intermetallic phases, structural analysis, solution treatment,mechanical properties.

1. Introduction

The characteristic properties of aluminium, good formability, good corrosionresistance, high strength stiffness to weight ratio, and recycling possibilities makeit as the ideal material to replace heavier materials (steel, cast iron or copper) inthe car [1]. More than half aluminium on the present produce in European Unioncomes from recycled raw material. The primary aluminium production needs alot of energy and constraints decision mining of bauxite. The European Unionhas big interest of share recycling aluminium and therefore increases interestabout secondary aluminium alloys and cast stock from them [2].

198 L. HURTALOVA, E. TILLOVA, M. CHALUPOVA

The replacement of primary aluminium with recycled has in recent years in-

creasing tendency. The recycled metal is a positive trend, because secondary alu-

minium produced from recycled metal requires only about 2.8 kWh/kg of metal

produced while primary aluminium production requires about 45 kWh/kg pro-

duced. The remelting of recycled metal saves almost 95% of the energy needed to

produce primary aluminium from ore, and, thus, triggers associated reductions

in pollution and greenhouse emissions from mining, ore refining, and melting.

Increasing the use of recycled metal is also quite important from an ecological

standpoint, since producing Al by recycling creates only about 5% as much CO2

as by primary production [3].

Due to the increasing utilization of recycled aluminium cast alloys, the qual-

ity of recycled Al-Si casting alloys is considered to be a key factor in selecting an

alloy casting for a particular engineering application. The mechanical properties

will be radically increasing by implementing adaptable alloying- and process

technology, leading to larger application fields of complex cast aluminium com-

ponents such as safety details. Generally, the mechanical and microstructural

properties of aluminium cast alloys are dependent on the composition; melt

treatment conditions, solidification rate, casting process and the applied thermal

treatment [4, 5]. The mechanical properties of Al-Si alloys depend, besides the

Si, Cu, Mg and Fe-content, more on the distribution and the shape of the silicon

particles [6]. The presence of additional elements in the Al-Si alloys allows many

complex intermetallic phases to form, such as binary phases (e.g. Mg2Si, Al2Cu),

ternary phases (e.g. β-Al5FeSi, Al2CuMg, AlFeMn, A17Cu4Ni and AlFeNi) and

quaternary phases (e.g. cubic α-Al15(FeMn)3Si2 and Al15Cu2Mg8Si6) [5, 6–10],

all of which may have some solubility for additional elements.

In AlSiCu cast alloy can form these intermetallic phases:

• Fe-rich intermetallic phases – Al5FeSi and Al15(FeMn)3Si2. The dominant

phase is phase know as beta- or β-needles phase Al5FeSi. This needle-shape

phase is more unwanted; because can bring high stress concentrations,

thereby increase crack imitation and decreasing the ductility [11, 12]. The

deleterious effect of Al5FeSi can be reduced by increasing the cooling rate

or superheating the molten metal. Another way that might by use to sup-

press the formation this monoclinic phase is converting the morphology by

the addition of a suitable “neutralizer” like Mn, Co, Cr, Ni, V, Mo and Be.

The most common addition has been Mn. Excess Mn may reduce Al5FeSi

phase and promote formation Fe-rich phases Al15(FeMn)3Si2 (know as

alpha- or α-phase) in form “skeleton like” or in form “Chinese script”.

This phase has according to some author’s cubic or hexagonal structure.

If Mg is also present with Si can phase called as pi- or π-phase form –

Al5Si6Mg8Fe2. Al5Si6Mg8Fe2 has script-like morphology [11–13].

THE STRUCTURE ANALYSIS OF SECONDARY (RECYCLED) ALSI9CU3. . . 199

• Cu-rich intermetallic phases – Al2Cu, Al-Al2Cu-Si and Al5Mg8Cu2Si6[11–14]. In unmodified alloys copper is present primarily as Al2Cu or Al-Al2Cu-Si phase, in modified alloys as Al5Mg8Cu2Si6. The average sizeof the copper phase decreases upon Sr modification. The Al2Cu phase isoften observed to precipitate both in a small blocky shape with microhard-ness 185 HV 0.01. Al-Al2Cu-Si phase is observed in very fine multi-phaseeutectic-like deposits with microhardness 280 HV 0.01 [5, 11, 14, 15].

Influence of intermetallic phases to mechanical and fatigue properties de-

pends on size, volume and morphology these phases [16]. The formation of these

phases should correspond to successive reactions during solidification with an

increasing number of phases involved at decreasing temperature. In practice,

Backerud et al. [17] identified five reactions in Al-Si-Cu alloy:

609◦C: α-dendritic network;

590◦C: Liq. → α-phase + Al15Mn3Si2 + Al5FeSi;

575◦C: Liq. → α-phase + Si + Al5FeSi;

525◦C: Liq. → α-phase + Al2Cu + Al5FeSi + Si;

507◦C: Liq. → α-phase + Al2Cu + Si + Al5Mg8Si6Cu2.

The quality and the tolerances of compositional secondary alloys are very

important, therefore are still under investigation of many academicals and indus-

trial projects. The purpose of the present article is to investigate microstructure

of cast Al-Si alloy (without and with heat treatment) prepared by recycling with

combination different analytical techniques (light microscopy upon black-white,

scanning electron microscopy (SEM) upon deep etching and energy dispersive

X-ray analysis (EDX)). As well as changes of the mechanical properties, which

are depending on the microstructure changes.

2. Experimental work

For investigation a microstructure was used the AlSi9Cu3 cast alloy with

chemical composition 9.4% Si, 2.4% Cu, 0.9% Fe, 0.28% Mg, 0.24% Mn, 1.0%

Zn, 0.03% Sn, 0.09% Pb, 0.04% Ti, 0.05% Ni, 0.04% Cr (wt. %). The chemical

analysis of cast alloy was carried out using an arc spark spectroscopy. The

experimental alloy (prepared by recycling of aluminium scrap) was received

in the form of 12.5 kg ingots. Experimental material was molten into the chill

mould (chill casting) (Fig. 1). The melting temperature was maintained at 760◦C

±5◦C. Molten metal was purified with salt AlCu4B6 before casting and was not

modified or grain refined.


a)

b)

Fig. 1. Metallic mould and molten semi-product: a) metallic mould with semi-product,b) detail of semi-product.

AlSi9Cu3 cast alloy has lower corrosion resistance and is suitable for high

temperature applications (dynamic exposed casts, where are not so big require-

ments on mechanical properties) – it means to max. 250◦C. The AlSi9Cu3 alloy

has these technological properties: tensile strength (Rm = 240–310 MPa), off-

set 0.2% yield stress (Rp0.2 = 140–240 MPa), however the low ductility limits

(A5 = 0.5–3%) and hardness HB 80–120 [18, 19].


Microstructural characterization was performed using light microscope Neo-

phot 32 and SEM observation with EDX analysis using scanning electron mi-

croscope VEGA LMU II, while phase microanalysis was performed using energy

dispersive X ray spectroscopy EDX (EDX analyzer Brucker Quantax). The sam-

ples for metallographic observations (1.5× 1.5 cm) were prepared by standards

metallographic procedures (wet ground, polished with diamond pastes, finally

polished with commercial fine silica slurry – STRUERS OP-U and etched by

standard reagent (Dix-Keller, 0.5% HF). Some samples were also deep-etched

in order to reveal the three-dimensional morphology of the silicon phase and in-

termetallic phases for 30 s in HCl solution. The specimen preparation procedure

for deep-etching consists of dissolving the aluminium matrix in a reagent that

will not attack the eutectic components or intermetallic phases. The residuals

of the etching products should be removed by intensive rinsing in alcohol. The

preliminary preparation of the specimen is not necessary, but removing the su-

perficial deformed or contaminated layer can shorten the process. Same pictures

were made with using backscattered electrons. The backscattered electrons are

beam electrons that are reflected from the sample by elastic scattering. BSE

are often used in analytical SEM, because the intensity of the BSE signal is

strongly related to the atomic number of the specimen, BSE images can provide

information about the distribution of different elements in the sample [16].

For better mechanical properties of Al-Si alloys is good to use a heat treat-

ment. Mechanical and fatigue properties of aluminium cast depends on size,

volume and morphology of intermetallic phases and silicon particles [16]. Dur-

ing heat treatment the morphology of intermetallic phases and silicon particles

was change and therefore was use solution treatment of AlSi9Cu3 alloy. Heat

treatment consist of solution treatment at temperature 505, 515 and 525◦C with

holding time 2, 4, 8, 16 and 32 hours, than water quenching at 40◦C and nature

aging for 24 hours on air.

3. Results of experimental work

AlSi9Cu3 belongs to hypoeutectic aluminium cast alloys because contains

9.4% of Si. The Fig. 2 shows as-cast microstructure of the experimental sec-

ondary AlSi9Cu3 cast alloy. The analyzed microstructure contains primary alu-

minium dendrites (α-phase – light grey – 1), eutectic (mixture of α-matrix and

spherical dark grey Si-particles – 2) and variously type’s Cu- and Fe-rich inter-

metallic phases (3, 4), that are concentrated mainly in the interdendritic spaces.

In view of the grey scale values in the SEM secondary electron images are higher

(brighter) for the higher atomic number of the elements, phases containing Cu

and/or Fe are brightest (Fig. 2b).


a) etch. Dix-Keller

b) deep-etch., SEM, BSE

Fig. 2. Microstructure of AlSi9Cu3 cast alloy.

3.1. Eutectic and eutectic silicon

The eutectic is mixture of α-matrix and Si particles. The α-matrix precip-

itates from the liquid as the primary phase in the form of dendrites and is

comprised of Al and Si (Fig. 2, Fig. 3a). Silicon is an anisotropic phase.


a) α-phase b) eutectic Si

etch. Dix-Keller etch. Dix-Keller

deep etch. HCl, SEM deep etch. HCl., SEM

Fig. 3. Eutectic and eutectic Si in as-cast structure of AlSi9Cu3 cast alloy.

Experimental material was not grain refined and not modified so eutectic Si

grows in a faceted manner along preferred crystallographic directions according

to the twin plane re-entrant edge mechanism (TPRE-mechanism) as platelets

(Fig. 3b). Most likely Si-platelets grew epitaxial from the surrounding primary

aluminium dendrites. This result is in accordance with reports for unmodified

Al-Si alloys.


a) 505◦C/4 h

etch. Dix-Keller deep etch. HCl., SEMb) 515◦C/4 h

etch. Dix-Keller deep etch. HCl., SEMc) 525◦C/4 h

etch. Dix-Keller deep etch. HCl., SEM

Fig. 4. Eutectic Si after heat treatment of AlSi9Cu3 cast alloy.


The mechanical properties of cast component are determined largely by the

shape and distribution of Si particles and intermetallic phases in α-matrix.

This plate-like type of morphology of eutectic Si is not good for mechanical

properties, because Si platelets are hard but brittle and can crack exposing

the soft α-matrix. Therefore are needs to affect this morphology with the ap-

propriate manner. The kinetics of Si morphology transformation is influencing

with the solution treatment (under certain conditions). Heat treatment affects

the precipitates size, shape and distribution in a cast component too [20]. The

spheroidization process of Si particles takes place in two stages with application

of solution treatment: a) fragmentation or dissolution of the eutectic Si branches;

b) spheroidization of the separated branches [21, 22]. Optimum tensile, impact

and fatigue properties are obtained with small, spherical and evenly distributed

particles. Silicon also imparts heat treating ability to the casting through the

formation of compounds with Mg, Fe and Cu. For that reason the AlSi9Cu3

cast alloy was heat treated.

The effect of solution treatment on morphology of eutectic Si is demonstrated

in Fig. 4. The changes in morphology of eutectic Si observed after heat treat-

ments are documented for holding time of 4 hours. Eutectic Si without heat

treatment (untreated state) occurs in platelets form (Fig. 3b). After solution

treatment by temperature of 505◦C we noted that the platelets were fragmen-

tized into smaller platelets with spherical edges (Fig. 4a). The spheroidized pro-

cess dominated at 515◦C. The smaller Si particles were spheroidized to rounded

shape, see Fig. 4b. By solution treatment at 525◦C the spheroidized particles

gradually grew larger (coarsening) (Fig. 4c).

3.2. Fe-rich intermetallic phases

Iron is one of the most critical alloying elements, because Fe is the most

common and usually detrimental impurity in cast Al-Si alloys. The Fe impurity

in Al-Si cast alloys results mainly from the use of steel tools and scrap materials

[10, 12, 23].

The solubility of iron is very low in aluminium alloys so most iron forms in-

termetallic phases. According to [24], the two main types of Fe-rich intermetallic

phases occurring in this AlSi9Cu3 alloy are Al5FeSi and Al15(FeMn)3Si2. Sig-

nificant levels of Fe (e.g. > 0.5%) can change the solidification characteristics

of Al-Si alloys by forming pre- and post-eutectic Al5FeSi phase [6, 11]. Al5FeSi

phases precipitate in the interdendritic and intergranular regions as platelets

(appearing as needles in the metallographic microscope – Fig. 5a). Long and

brittle Al5FeSi platelets (more than 500 µm) can adversely affect mechanical

properties and also lead to the formation of excessive shrinkage porosity de-


a) Al5FeSi b) Al15(FeMn)3Si2

etch. 0.5 HF etch. 0.5 HF

deep etch. HCl deep etch. HCl, BSE

Fig. 5. Morphology of Fe-rich intermetallic phases in as-cast structureof AlSi9Cu3 cast alloy, SEM.

fects in castings [25]. Taylor [11] further suggested that the formation of large

β platelets at high Fe-contents facilitates the nucleation of eutectic Si, there-

fore leading to a rapid deterioration of the interdendritic permeability. The β

platelets appeared to be the main nucleation sites for the eutectic Si and Cu-rich


a)

b)

c)d)

Fig.6.EffectofheattreatmentonFe-richphasesofAlSi9Cu3castalloy:a)505◦C/4h,etch.Dix-Keller,

b)515◦C/4h,etch.Dix-Keller,c)525◦C/4h,etch.Dix-Keller,d)changesinaverageareaofFe-richphases.


phase. Nucleation of Si and Al2Cu may occur on large Al5FeSi platelets. Phase

with cubic crystal structure – Al15(FeMn)3Si2 is considered less harmful to the

mechanical properties than β phase [26, 27]. This phase (Fig. 5b) has a compact

morphology “Chinese script” or skeleton-like, which does not initiate cracks in

the cast material to the same extent as the Al5FeSi (Fig. 5a).

The Fe-rich particles can be twice as large as the Si particles, and the cool-

ing rate has a direct impact on the kinetics, quantities and size of Fe-rich in-

termetallic present in the microstructure. In experimental recycled AlSi9Cu3

cast alloy that contains less than 0.9% of Fe and 0.24% of Mn were observed

Al5FeSi needles (Fig. 5a) – on deep etcher samples plate-like form (Fig. 5a) and

Al15(FeMn)3Si2 – skeleton-like form (Fig. 5b). In experimental material was

satisfied condition Fe :Mn = 2 : 1, therefore intermetallic needles phases were

observed in a few isolated cases.

Heat treatment was use for affecting the size of Fe-rich phases, because the

shape and size of iron compounds is more influential than the quantity of those

iron compounds. The evolution of the Fe-rich phases during solution treatment

is described in Fig. 6. Al5FeSi phase is dissolved into very small needles (difficult

to observe). The Al15(MnFe)3Si2 phase was fragmented to smaller skeleton par-

ticles. In the untreated state Al15(FeMn)3Si2 phase has a compact skeleton-like

form (Fig. 5b). Solution treatment of this skeleton-like phase at 505◦C tends to

fragmentation (Fig. 6a) and at 515 or 525◦C to spheroidization and segmenta-

tion (Fig. 6b, c).

For the confirmation that solution treatment reduces Fe-rich phases area and

affects its morphology was used the quantitative metallography. Quantitative

metallography was carried out on an Image Analyzer NIS – Elements to quantify

Fe-rich phases (average area) morphology changes, during solution treatment.

Figure 6d shows the changes in the average area of Fe-rich phases during solution

treatment. The maximum average area of Fe-rich phases was observed in as-cast

samples (2 495 µm2). By increasing the solution temperature the average area

of Fe-phases drop to (the increasing temperature of solution treatment causes

dropping the average area of Fe-phases to 320 µm2 by 515◦C). With a prolonged

solution treatment time more than 8 h, the extent of dissolution of Fe-rich phases

changed little.

3.3. Cu-rich intermetallic phases

Half or more of the copper is found as a component of intermetallic com-

pounds [28]. Cu intermetallic phases are in aluminium alloys forming such as

Al2Cu with tetragonal crystal structure, which solidified in two morphologies

after Al-Si eutectic reaction. The first are as massive or blocky form (Al2Cu


– Fig. 7a-1, 7c) with high copper concentration ∼38–40 % Cu and second are

as fine ternary eutectic form (Al-Al2Cu-Si – Fig. 7a-2, 7b, 7d). The latter type

is more pronounced in the unmodified alloy and was observed either as sepa-

rate eutectic pockets or precipitated on pre-existing Si-particles or Fe-phases

[26, 28, 29]. In experimental material were observed both types of Cu-rich in-

termetallic phases (Fig. 7).

a) b)

c) d)

Fig. 7. Morphology of Cu-rich intermetallic phases in as-cast structure of AlSi9Cu3 cast alloy:a) 1-Al2Cu, 2- Al-Al2Cu-Si, etch. Dix-Keller, SEM, b) Al-Al2Cu-Si, deep etch. HCl, SEM,c) detail of Al2Cu phase, etch. Dix-Keller, d) detail of Al-Al2Cu-Si phase, etch. Dix-Keller.

The increasing level of Cu improves the strength of the aluminium alloythrough the formation of Cu based precipitate during heat treatment. The effectof heat treatment on morphology of Cu-rich phases was followed by optical and


a)

b)

c)d)

Fig.8.EffectofheattreatmentonCu-richphasesofAlSi9Cu3castalloy:a)505◦C/4h,etch.Dix-Keller,

b)515◦C/4h,etch.Dix-Keller,c)525◦C/4h,etch.Dix-Keller,d)changesinaverageareaofCu-richphases.


electron microscopy. Morphology changes of Al-Al2Cu-Si during heat treatmentare demonstrated in Fig. 8. The changes of morphology of Al-Al2Cu-Si observedafter heat treatment are documented for holding time 4 hours.Al-Al2Cu-Si phase without heat treatment (as-cast state) occurs in form

compact oval troops (Fig. 7). After solution treatment at temperature 505◦Cthese phase disintegrated into smaller segments. The amount of Al-Al2Cu-Siphase decreases. This phase is gradually dissolved into the surrounding Al-matrix with an increase in solution treatment time (Fig. 8a). By solution treat-ment 515◦C was this phase observed in the form coarsened globular particles andthese occurs along the black needles, probably Fe-rich Al5FeSi phase (Fig. 8b).By solution treatment 525◦C was this phase documented in the form moltenparticles with homogenous shape (Fig. 8c).The changes of average area of Cu rich phases were confirmed by using the

quantitative metallography, too. Figure 8d shows average area of Cu-rich phasesobtained in solution heat treated samples. Maximum average area of Al-Al2Cu-Si phase was observed by temperature solution treatment at 505◦C with holdingtimes 2 hours (357µm2). Minimum average area of Al-Al2Cu-Si phase particlewas observed by temperature solution treatment at 515◦C (0.277 µm2). It isevident that heating at temperatures below the final solidification temperature(505◦C, 515◦C and 525◦C) results in dissolution of Al-Al2Cu-Si phase [29–31].Solution treatment at 525◦C apparently causes a marked change (Fig. 8). This,however, is attributed to the melting of the Al-Al2Cu-Si, rather than to itsdissolution. Dissolution and melting of Al2Cu phase in AlSi9Cu3 alloy has beenstudied in detail by Samuel [32]. When the AlSi9Cu3 alloy is solution treatedat temperature about the melting point of the eutectic (Al+Al2Cu) phase, e.g.525–540◦C, the Al-Al2Cu-Si particles may undergo incipient melting even afterperiods as 4 hours [29–31].

3.4. SEM image and X-ray analysis

The SEM image and X-rays analysis were used for a complete structuralanalysis of experimental material. Figure 9 shows typical example: a SEM imageand X-rays analysis of Al-Al2Cu-Si.Structural analysis identified of recycled (secondary) AlSi9Cu3 cast alloy

as basic structural elements: α-phase, Si platelets, Fe-rich intermetallic phases:needles – Al5FeSi (but in a small volume); skeleton-like Al15(FeMn)3Si2 phaseand Cu-rich intermetallic phase: Al2Cu (but in a small volume); Al-Al2Cu-Siternary eutectic. The EDX analysis revealed that the identified Cu-rich and Fe-rich intermetallic phases by using light microscopy are really these intermetallicphases, because chemical composition of these phases was confirmed by EDXanalysis.


a)

[Fig. 9]


b)

[Fig. 9]


c)

Fig. 9. Analysis of intermetallic phases in as-cast state of AlSi9Cu3 cast alloy, SEM:a) point X-ray analysis, b) line X-ray analysis, c) SEM image analysis.

3.5. Changes of mechanical properties causes with changes of structure

Heat treatment is one of the major factors used to enhance the mechanicalproperties of heat-treatable Al-Si alloys, through an optimization of both solu-tion and aging heat treatments. The solution treatment homogenises the caststructure and minimizes segregation of alloying elements in the casting. Seg-regation of solute elements resulting from dendritic solidification may have anadverse effect on mechanical properties.Changes of microstructural parameters cause changes in mechanical proper-

ties during solution treatment. Solution treatment performs tree roles: homog-enization of as-cast structure; dissolution of certain intermetallic phases suchas Al2Cu; changes the morphology of eutectic Si and intermetallic phases byfragmentation, spheroidization and coarsening, thereby improving mechanicalproperties.After heat treatment were samples subjected for mechanical test (strength

tensile and Brinell hardness). Influence of solution treatment and changes ofmicrostructural parameters on mechanical properties are shown on Fig. 10 and


Fig. 10. Changes of strength tensile.

Fig. 11. After solution treatment tensile strength and hardness are remarkablyimproved, compared to the corresponding as-cast condition. Highest strengthtensile was 273 MPa for 515◦C/4 hours (Fig. 10). With further increase in solu-tion temperature more than 515◦C and solution time more than 8 hours, tensilestrength gently decreases during the whole solution period.

Fig. 11. Changes of Brinell hardness.

Results of hardness (Fig. 11) are comparable with results of tensile strength.Highest hardness was 124 HBS for 515◦C/2 hours. The hardness decreases dur-ing the temperature 525◦C due to melting of the Al-Al2Cu-Si phase by thistemperature [29–31].

4. Conclusion

Understanding metal quality is of great importance for control and predictionof casting characteristics. The results of optical and SEM studies of recycled(secondary) AlSi9Cu3 cast alloy are summarized as follows:

• Structural analysis identified as basic structural elements: α-phase, Si platelets,and intermetallic phases (Al15(FeMn)3Si2 in the skeleton-like form, Al5FeSi


in form needles and Cu-ternary eutectic Al-Al2Cu-Si, Al2Cu in a small blockshape).

• In experimental material are dominant: Cu-rich phase Al-Al2Cu-Si and Fe-phases Al15(FeMn)3Si2 (thanks to the presence of Mn). Chemical compositionof all phases was confirmed by EDX analysis.

• During heat treatment Si particles spheroidized. As the optimum temperatureof spheroidization the eutectic Si was specified the temperature 515◦C.

• The morphology and size of iron phases are highly dependent on the solutiontreatment. Platelets Fe-rich phases (Al5FeSi) are dissolved into very smallneedle phases. Skeleton-like Fe-rich phases (Al15(FeMn)3Si2) are fragmentedand dissolved (average area reduces from 2 495 to 320 µm2).

• Al-Al2Cu-Si phases are fragmented, dissolved and redistributed within α-matrix (average area of Cu-phases particle decreases from 9 995.5 µm2 to0.277 µm2) during heat treatment.

• Changes of microstructural parameters of AlSi9Cu3 cause changes in mechan-ical properties. The highest strength tensile was at a temperature of 515◦Cwith holding time 4 hours; the highest hardness at a temperature of 515◦Cwith holding time 2 and 4 hours. For this was defined as optimum regime ofsolution treatment for experimental samples from AlSi9Cu3 cast alloy usingin automotive industries regime: 515◦C with a holding time of 4 hours, waterquenching at 40◦C and nature aging for 24 hours on air. After heat treat-ment, casts for automotive industries have better mechanical properties as inan as-cast state.

Acknowledgment

The authors acknowledge the financial support of the projects No. 1/0841/11and No. 1/0460/11.

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Received February 25, 2013; revised version June 24, 2013.

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